Exhaust emissions of internal combustion engines, particularly diesel engines, contain regulated exhaust constituents, mainly nitrogen oxides (NOX) and soot particles. Such emissions are limited by federal laws and regulations in most countries. One common way to reduce nitrogen oxide emissions is to use an exhaust gas recirculation (EGR) system wherein a part of the exhaust gas is purposely returned to the combustion chamber. This action leads to lower peak combustion temperatures, which in turn reduces formation of NOX.
The typical modern diesel EGR system employs a so-called high pressure loop (HPL) system wherein a portion of engine exhaust is removed upstream of a turbine of a turbocharger. A pressure differential between exhaust and intake manifolds may be maintained to be positive in order to provide adequate EGR flow upon demand; the pressure differential may be controlled by various means, such as a variable geometry turbine or a backpressure valve. In some embodiments, the exhaust portion flows through an EGR cooler provided with a coolant medium, such as engine coolant or ambient air. From the cooler, the EGR flows through an EGR conduit into an EGR venturi tube (herein called a venturi) adapted to provide control feedback for managing the EGR flow rate. An EGR control valve directly controls the EGR flow rate, as the recirculated exhaust gas mixes with so-called cooled charge air before being inducted into the engine via the intake manifold.
In a heavy duty diesel engine environment, the EGR venturi can heat up to temperatures beyond designed operational limits of various electronic pressure sensors and associated wiring, particularly when the engine is operated at higher loads. Many solutions have been offered, including one provided in U.S. Pat. No. 7,921,830, which discloses a venturi containing liquid cooled internal chambers to manage operating temperatures within the physical venturi structure. The solution offered is relatively expensive, and may not be as effective as desired. A second solution is offered in U.S. Pat. No. 6,415,757, which discloses a double-walled chamber (FIG. 5) adapted to enclose temperature sensitive electronics, and to circulate cooling fluid through the chamber. A simpler and more conveniently assembled solution is desired.